This invention relates generally to medical diagnostic apparatus and methodology, and more specifically relates to x-ray scanning apparatus of the type utilized in computerized tomography.
Within very recent years, a relatively enormous degree of interest has been evidenced on the part of medical diagnosticians in a field now widely known as computerized tomography. In a typical procedure utilized in computerized tomography (or CT), an x-ray source and detector means are positioned on opposite sides of the portion of the patient which is to be examined. In the prior art these paired elements are made to transit across the body portion to be examined, while the detectors measure the x-ray absorption at the plurality of transmission paths defined during the transit process. Periodically as well, the paired source and detector means are rotated to a differing angular orientation about the body, and the transit process repeated. A very high number of absorption values may be yielded by procedures of this type, and the relatively massive amount of data thus accumulated may be processed by a digital computer--which crosscorrelates the absorption values to thereby derive absorption values for a very high number of points (typically in the thousands) within the section of the body being scanned. This point by point data may then be combined to enable reconstruction of a matrix (visual or otherwise) which constitutes an accurate depiction of the density function of the bodily section examined. The skilled diagnostician, by considering one or more of such sections, may diagnose various bodily elements such as tumors, blood clots, cysts, hemorrhages and various abnormalities, which heretofore were detectable, if at all, only by much more cumbersome and, in many instances, more hazardous (from the viewpoint of the patient) techniques.
While apparatus of the aforementioned type has therefore represented powerful diagnostic tools, and has been deemed great advances in the radiography art, apparatus heretofore designed and commercially available has suffered from many of the shortcomings incident to first generation devices. Thus, for example, it may be noted that acquisition of the raw data obtained as an incident of the discussed techniques frequently entailed an undesirably long period--in which among other things subjected a patient to both inconvenience and stress. The patient's inability to remain rigid for such a lengthy period, also could lead to blurring of the image sought to be obtained.
The prior art apparatus furthermore is not well adapted to successive use with a large number of patients. For example, to the extent rotational scanning has been utilized, such apparatus has in general been designed to effect a single rotational cycle, with intertransmission of the various excitation potentials for the x-ray tube, and the signal outputs for the detectors being effected through means which are not compatable with continuously rotating configurations. Aside from the inconvenience, inefficiency and delays that are incident to stopping and starting of the equipment, such procedures can adversely affect system components. For example, the spinning anodes used in many X-ray tubes possess a very high moment of inertia in consequence of their rapid rotation, and this augments the stresses imposed on such elements by sudden velocity changes in their reference frame.
Such prior devices furthermore have not been markedly adapted to use in rapidly producing a consecutive series of cross-sectional views through a patient, or portion of a patient being examined.
In other instances, the amount of radiation received by the patient during examination was excessive--due to certain failings in the types of X-ray techniques and procedures utilized.
In an equally significant aspect of the prior art devices, it has been observed that the picture (or output data) quality resulting from use of such devices was less than fully acceptable--particularly where data is obtained over an extended period. A principal cause of this difficulty is the fact that such apparatus is indeed utilized over the course of an extended period, e.g. as is the practice in use of these devices in large institutional environments. During the extended periods incident to such use, temperature and/or time-generated drifts in the electronic processing circuits, i.e., the circuits utilized with the detectors, can cause changes among the various processing channels, with resultant introduction of erroneous information into the signal outputs provided to the computer.
In a copending application of John M. Pavkovich and Craig S. Nunan, Ser. No. 643,894 filed on Dec. 23, 1975 entitled "Tomographic Apparatus and Method for Reconstructing Planar Slices from Non-absorbed Radiation", and as well in the similarly copending application of John M. Pavkovich entitled "Apparatus and Method for Reconstructing Data", filed on Dec. 23, 1975, under Ser. No. 643,896, both applications of which are assigned to the same assignee as is the present application, apparatus and methodology are disclosed which alleviate certain of the aforementioned problems, most notably including the lengthy period that has heretofore been involved in computer processing of the raw data provided by the detectors. The apparatus therein disclosed utilizes a fan beam source of radiation coupled with application of a convolution method of data reduction, with no intervening reordering of fan rays, to thereby eliminate the errors and delays in computation time which would otherwise be involved in such reordering. The radiation source and the detector means are positioned on opposite sides of the portion of the patient to be examined and these elements are made to rotate through a revolution or portion thereof while the detectors measure the radiation absorption at the plurality of transmission paths defined during the rotational process.
In accordance with the foregoing, it may be regarded as an object of the present invention to provide scanning apparatus for use in computerized tomography systems or the like, which is adapted to rapid and virtually continuous use in diagnostic treatment of a series of patients, and which, by virtue of the continuous operation thereof, avoids the physical stressing of system components which can result as an incident of starting and stopping of the rotatable assemblies utilized with such apparatus.
It is a further object of the present invention to provide apparatus of the aforementioned type which is adapted for use in producing a series of successive cross-sectional views through a portion of a patient being examined.
It is a yet further object of the present invention, to provide apparatus of the aforementioned type wherein the quality of the data generated, and therefore the resulting capabilities for image reconstruction, can be markedly improved by incorporation of calibration circuitry, which enables compensation to be effected for drift in the electronic processing circuits resulting from temperature or time-induced changes in circuit components.
It is a still further object of the invention, to provide scanning apparatus for use in computerized tomography systems or the like, wherein the signal processing and conditioning circuitry is in close physical proximity to the detector elements on the rotating assembly of the apparatus, thereby minimizing noise and spurious signals, as may, e.g. be induced by the circuitry associated with the radiation source used in the apparatus.
It is a yet additional object of the present invention, to provide scanning apparatus for use in computerized axial tomography systems, which includes interconnection means movable with the portion of the said apparatus subject to rotation, whereby the various signal information proceeding to the reconstruction and control station and, as well, the power and control signals for the radiation source, may be interfed to and from the rotating portions of the apparatus in simple and effective fashion, and without any requirement for periodically stopping or reversing system rotation.